1. Field of the Invention
The present invention relates to a process for stabilizing certain fluorophosphite ligands against degradation. More particularly, the present invention relates to the addition of an epoxide to a homogeneous reaction mixture containing certain fluorophosphite ligands and a Group VIII transition metal catalyst to enhance the stabilization of the fluorophosphite ligands and prevent their degradation. More particularly, the fluorophosphite ligands and rhodium catalyst are used in hydroformylation of various @-olefins for producing aldehydes.
2. Background of the Invention
The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. In many of the hydroformylation processes, a catalyst is used that includes a phosphorous containing compound in combination with a Group VIII metal, such as cobalt and rhodium being particularly preferred.
The most extensive use of the hydroformylation reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amount of the normal aldehyde product to the amount of the iso aldehyde product typically is referred to as the normal to iso (N:I) or the normal to branched (N:B) ratio. In the case of propylene, the normal- and iso-butyraldehydes obtained from propylene are in turn converted into many commercially-valuable chemical products, such as, for example, n-butanol, 2-ethyl-hexanol, n-butyric acid, iso-butanol, neo-pentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, and the mono-isobutyrate and di-isobutyrate esters of 2,2,4-trimethyl-1,3-pentanediol. The hydroformylation of higher xcex1-olefins such as 1-octene, 1-hexene and 1-decene yields aldehyde products which are useful feedstocks for the preparation of detergent alcohols and plasticizer alcohols. The hydroformylation of substituted olefins such as allyl alcohol is useful for the production of other commercially valuable products such as 1,4-butanediol.
U.S. Pat. No. 3,239,566, issued Mar. 8, 1966, to Slaugh and Mullineaux, discloses a low pressure hydroformylation process using trialkylphosphines in combination with rhodium catalysts for the preparation of aldehydes. Trialkylphosphines have seen much use in industrial hydroformylation processes but they typically produce a limited range of products and, furthermore, frequently are very oxygen sensitive.
U.S. Pat. No. 3,527,809, issued Sep. 8, 1970 to Pruett and Smith, discloses a low pressure hydroformylation process which utilizes triarylphosphine or triarylphosphite ligands in combination with rhodium catalysts. The ligands disclosed by Pruett and Smith, although used in many commercial applications, have limitations due to oxidative and hydrolytic stability problems. Since these early disclosures, numerous improvements have been made to increase the catalyst stability, catalyst activity and the product ratio with a heavy emphasis on yielding linear aldehyde product. A wide variety of monodentate phosphite and phosphine ligands, bidentate ligands such as bisphosphites and bisphosphines as well as tridentate and polydentate ligands have been prepared and disclosed in the literature.
U.S. Pat. No. 5,840,647 issued Nov. 24, 1998 to Puckette et al. discloses a fluorophosphite-containing catalyst system having a catalyst combination of one or more transition metals selected from the Group VIII metals and/or rhenium and one or more fluorophosphite compounds having the general formula: 
wherein R1 and R2 are hydrocarbyl radicals which contain a total of up to about 40 carbon atoms and wherein the ratio of gram moles fluorophosphite ligand to gram atoms transition metal is at least 1:1. As will be understood by those skilled in the art, such fluorophosphite compounds of structure (I) are also known in the chemical literature as fluorophosphite esters and such terms are used interchangeably herein.
A problem recently recognized in hydroformylation of xcex1-olefins is that phosphite ligands can be depleted through reaction with components in the hydroformylation reaction mixture. For example, U.S. Pat. No. 4,496,768 postulates the formation of adducts of certain phosphites with aldehydes. U.S. Pat. Nos. 4,496,768 and 4,482,749 disclose certain cyclic phosphite ligands are capable of operating for extended periods of time in hydroformylation reaction mixtures with little or no degradation of the ligand.
It has been observed that the ligand undergoes slow hydrolysis in the presence of water in the reaction mixture. The decomposition products then react with the aldehyde product and additional water in the reaction mixture in a series of steps to form hydroxyalkylphosphonic acids. The acids so formed catalyze further hydrolysis of the ligand. The cascading effect causes very rapid hydrolysis of the phosphite ligand remaining in the reaction solution and leads to a significant loss of the phosphite ligand.
U.S. Pat. No. 5,288,918, issued to Maher et al. on Feb. 22, 1994, discloses that catalytic deactivation is believed primarily or at least partly due to the formation of a class of diorganophosphite by-products which can best be described as decomposition by-products of alkyl (1,1xe2x80x2-biaryl-2,2xe2x80x2-diyl) phosphites, the alkyl radical corresponding to the particular n-aldehyde produced by the hydroformylation process and the (1,1xe2x80x2-biaryl-2,2xe2x80x2-diyl) portion of the phosphite being derived from the organobisphosphite ligand employed. Maher teaches that the adverse effects of such compounds can be reversed or minimized by carrying out the hydroformylation process in the presence of weakly acidic compounds, added water or mixtures of both. The weakly acidic compounds have a pKa of from about 1.0 to about 12.
U.S. Pat. No. 5,756,855, issued on May 26, 1998 to Abatjoglou et al., discloses stabilizing phosphite degradation by the addition of certain metals. Abatjoglou discloses adding a Group VIII metal (other than rhodium) in an amount sufficient to reduce the rhodium-catalyzed decomposition of the phosphite during the hydroformylation process.
U.S. Pat. No. 5,364,950, issued on Nov. 15, 1994 to Babin et al., discloses stabilizing a triorganophosphites, diorganophosphites and bis-phosphites phosphite ligand wherein the phosphorous moiety is bound to three oxygen moieties. However, the ""950 patent is silent as to what effect, if any, an epoxide may have to stabilize a fluorophosphite ligand in which a secondary acid, i.e., hydrofluoric acid, may be present in the reaction mixture.
Accordingly, there is a need for a process for stabilizing certain fluorophosphite ligands against degradation when used in a hydroformylation reaction.
Briefly, the process of the present invention is for stabilizing a fluorophosphite ligand in a hydroformylation reaction mixture containing an olefinic compound, carbon monoxide, hydrogen, a catalyst composition comprising a combination of a transition metal selected from the Group VIII metals and one or more fluorophosphite compounds having the general formula: 
wherein R1 and R2 are hydrocarbyl radicals which contain a total of up to about 40 carbon atoms by adding to the reaction mixture an epoxide.
Surprisingly, it was found that the addition of an epoxide to the hydroformylation reaction mixture was effective in markedly lowering the production of phosphorous acids and hydrofluoric acid without detrimental reaction with the aldehyde product.
It is an object of the present invention to provide a process for stabilizing a fluorophosphite ligand in a hydroformylation reaction mixture. This and other objects and advantages of the present invention will become more apparent to those skilled in the art in view of the following description. It is to be understood that the inventive concept is not to be considered limited to the constructions disclosed herein but instead by the scope of the appended claims.